This invention relates to a continuous process for the reaction of solid metal carbonates, bicarbonates and oxides with a hydrogen halide gas in a true fluidized state with the production of a solid having a composition composed of the metal and the halide ion. The invention relates more particularly to the manufacture of calcium chloride, magnesium chloride, zinc chloride and chlorides of iron in an energy efficient non-aqueous medium using conventional or true fluidized bed technology and counter current flow generally but not exclusively between the solid flowing downward by gravity and the upward moving gas. The process is unique in that it is basically self-controlling, that is, the feed rate of the solids and gas and the design of the vessel control the production rate and degree of conversion of the solids. No elaborate controls are required, little or no recycling of reaction gas or product are necessary since the counter current aspect of the process is such that complete conversion of the solid is achieved, the exiting gas is essentially free of the hydrogen halide component of the feed gas, and the particle size of the product remains essentially the same as the original solid feed, although some finer particles are produced.
Halogens, with some exceptions, chemically behave generally in the same manner. The reactions of hydrochloric acid therefore are similar in many respects to those of the acids of the other halogens. Anhydrous hydrogen chloride is relatively inert because of the high kinetic barrier to fission of the Hxe2x80x94Cl bond. Anhydrous hydrogen chloride however has an extremely high affinity for water, even if the water is in the vapor or gaseous state, which was demonstrated as early as 1860 by William Odling and reported in Vol. 1 of xe2x80x9cThe Chemical Newsxe2x80x9d. This is very important when the reactions in this teaching are considered. It is contemplated that the industrial gases employed in the teaching will not be anhydrous and will contain some water vapor and therefore will be significantly more reactive because of the effect of this moisture on assisting the fission of the H-Cl bond. In addition when these acid reactions proceed, water, whether gas or vapor, will be liberated and increase the reaction rate.
CaCO3+2HCL(g)xe2x86x92CaCl2+CO2↑+H2O(g)xcex94H=xe2x88x928.82 kcal/mol
The reaction of the metal compounds in the instant invention all produce water in the gaseous or vapor phase and because the reactions are exothermic and the heat exchange between solid and gas in a true or conventional fluidized bed is very efficient, condensation of this water is substantially unlikely in the process to be described.
For many years calcium chloride was primarily produced as a by-product of soda ash manufacture by the Solvay Process. In this process the recovery of (NH3) Ammonia from the process liquors containing ammonium chloride is economically essential. This is accomplished by adding milk of lime Ca(OH2) to the process liquors thereby producing calcium chloride.
2NH4Cl+Ca(OH)2xe2x86x92CaCl2+2NH3(g)+2H2O(g)
The calcium chloride liquors were then clarified, concentrated by evaporation, crystallized and melted to produce flake calcium chloride. With the demise of soda ash production by the Solvay Process in the USA, due to the mining of the Trona in Wyoming, significant production of calcium chloride was lost. The last remaining Solvay Process plant in North America at Amherstburg, Ontario in Canada has now been shut down for the same reason. Large tonnage is also produced through recovery from saline solutions by the Dow Chemical Companies in Michigan.
A significant percentage of USA production has now been replaced by the reaction of hydrochloric acid with calcium carbonate to produce a calcium chloride solution. The solutions produced require concentration by evaporation and crystallization processes to produce crystals of calcium chloride and melting (782xc2x0 C.) of the crystals to produce flake calcium chloride. Both of these operations are energy and capital intensive which in a rising energy-cost environment significantly increases the cost of production. The hydrochloric acid is produced in large quantities as a byproduct from chlorinated hydrocarbon production and off gases from chlorine production and other operations.
Loots and Van Goftberg teach in Canadian patent CA 2,038,021 three methods for producing calcium chloride, two of which are identical in almost all respects, from anhydrous gases containing hydrogen chloride, chlorine, and mixtures of these gases. The first method consists of a number of fixed beds of CaCO3, or Ca(OH)2 or CaO in series and through which the anhydrous gas or mixture of anhydrous gases are passed for a period of time until the conversion to calcium chloride is complete in the first bed in the series. This bed is then removed from the series to be unloaded and recharged, while the next bed in the series becomes the first in the series. While the discussion of the process indicates that it is possible in principle for reaction (page 1, line 10) CaO+HClxe2x86x92CaCl2+H2O to proceed at gas and bed ambient temperature, the inventors then state that (page 2, line 20) it will not be possible to achieve the desired bed temperatures under these conditions, which leads one to the conclusion that the reaction will not proceed without heat input to the bed and gas. Since reaction (1) outlined in the teaching has thermodynamically the highest xcex94H it is also presumed that none of the other reactions involving anhydrous hydrogen chloride (HCl)g or chlorine (Cl2)g with calcium hydroxide (Ca(OH)2) or calcium carbonate CaCO3 will proceed at ambient temperature. Some of the major disadvantages of this process are that significant labor would be required to load and unload the reactors with raw materials and finished product. It was disclosed on page 7, lines 27-28 that for the calcium carbonate hydrogen chloride test that the finished product was a hard plug which required crushing. This is a major disadvantage since removal from a commercial vessel would require significant labor and crushing would produce large amounts of undesirable fines.
Another disadvantage is that the higher-pressure drop across the bed requires more energy to increase the gas pressures. In addition, more expensive, heavier walled vessels are required because of the higher pressure, increasing the capital investment.
A further disadvantage is determining when full conversion to calcium chloride is attained since the product is contained in a closed pressurized vessel. Still another disadvantage is that a large number of vessels are required to insure continuous operation while one or more vessels are being loaded and unloaded, adding considerably to capital cost.
Two additional embodiments of the Loots and Van Gottberg invention both somewhat alike and described as a xe2x80x9cfluidized bedxe2x80x9d, teach a process in which either calcium carbonate, oxide, or hydroxide are contained in a reaction vessel or riser and reacted with hydrochloric acid and or chlorine from which the spent gas and the finished calcium chloride (entrained in the gas stream) is withdrawn. A cyclone or other separating devise is employed to remove the finished product from the gas. Part of the gas stream is recycled to provide reheat to the feed gas. Particle size is in the rage of 50 to 300 microns. This is a very fine product that has little or no commercial value and requires melting (782xc2x0 C.) and flaking or prilling if it is to be sold as a solid. Significant capital investment and energy use is required to accomplish this by way of high-pressure steam generation and flakers or prill towers.
Both processes are described as a xe2x80x9cfluidized processxe2x80x9d, a term which is often used to describe spouting beds similar to those produced in a xe2x80x9cWursterxe2x80x9d type apparatus or a fast moving gas stream containing or conveying entrained solids, or to describe a dense phase gas agitated bed in a state of substantial fluidity. While these may fall under the generic term xe2x80x9cfluidizedxe2x80x9d they are not true or conventional fluidized beds. In a conventional or true fluidized bed the solid particles are kept in a randomly moving fluidized condition by a stream of pressurized gas, which is forced through perforations of a support plate, causing the solid particles to move in a random bubbling fashion similar to a gently boiling liquid. These conditions permit the solids to flow and act like liquids and maintain a level like liquids. In U.S. Pat. No. 5,399,186; Mar. 21, 1995; column 4, line 44, Darrah et. al., go to some length to distinguish true or conventional fluidization as used in their teaching from the various types noted above. In U.S. Pat. No. 4,495,163; Jan. 22, 1985; column 3, line 34, Nguyen found it necessary to define fluidized beds generically to distinguish his teaching as follows, xe2x80x9cThe term fluidized bed as used herein is intended to include conventional fluid beds, fast moving fluid transport systems wherein the pellets are carried in the gas stream separated and returned to a point of introduction, spouting beds, etc.xe2x80x9d It is important to emphasize this distinction since true or conventional fluidization causes the solids to flow and act like liquids.
True fluidization as used in the instant invention is that which meets the definition outlined in the Darrah patent, which permits a continuous operation, the use of counter current gas and solid flows, which results in the production of high purity finished product, retention of crystal integrity, rapid conversion rates, simplicity of the apparatus, very efficient energy conservation, the elimination of environmentally controlled emissions and minimum capital investment. It excludes spouting beds, dense phase gas agitated beds, allutriated zones or fast moving transport or solid conveying systems since using such means other than that described as conventional or true fluidization will not accomplish the results described in the inventive process.
Operation of the process as described as the second embodiment (FIG. 2, reference 100) is somewhat unclear and as will be shown in a later discussion does not appear amenable to producing an effluent gas without HCl or Cl2 contamination or a finished product completely converted to calcium chloride. It is also very unclear as to how the inventors intended the process to operate. They apply various meanings to the word xe2x80x9cfluidizexe2x80x9d so that it is difficult to know precisely what is meant when the word is used. For example, on page 3 lines 18 to 25 there is no distinction made between a xe2x80x9cfluidized bedxe2x80x9d in a reaction vessel and xe2x80x9cwithdrawing an overhead stream containing spent gas and entrained calcium chloride particlesxe2x80x9d. Both of these processes cannot be performed at the same time since the lafter actions (gas conveying) requires much higher gas velocities than true fluidization. Data provided by the inventors page 20, lines 1 to 6 clearly show this. Page 11, line 15 outlines an experiment in which a so called xe2x80x9cfluidized bedxe2x80x9dwas simulated using small particles and a gas velocity of 3 m/sec which is a conveying velocity according to the inventors definition and which cannot fit the classical definition of a fluidized bed. Furthermore the inventors in page 21, lines 4 and 5 equate a gas with entrained solids with fluidization as follows xe2x80x9cthrough which solid particles in fluidized or entrained form can passxe2x80x9d.
FIG. 2 (reference 100) depicts a bed of particles described as being fluidized yet there is shown only a single gas entry, no perforated support plate or gas plenum is shown. The apparatus description does not include these essential elements for true fluidization so that it appears that the bed is not a true or conventional fluidized bed but a dense phase gas agitated bed. This conclusion is supported by the contradictory descriptions on page 10 (see lines 1, 2, and 9-11) that xe2x80x9can overhead stream comprising spent gas and calcium chloride particles exit the top of the vessel 102 since it is not possible to concurrently maintain either a true fluidized bed or a gas agitated bed with a gas velocity high enough to carry the particles out of the vessel.
The only process operation that supports the descriptions outlined is a batch process composed of a dense phase gas agitated bed of particles maintained in a state of minimum fluidity and which are contacted by the reactive gases for a long period of time after which the gas velocity is greatly increased to vacate the vessel. The vessel would then be recharged through the venturi mechanism depicted. There are many serious disadvantages to this process including environmental degradation and substantial capital investment as will be described following the discussion of the third embodiment of the process. If the so-called xe2x80x9cfluidizedxe2x80x9d bed is intended to be a spouting bed or a circulating bed the same conditions as previously described will exist.
The drawings and description for the third embodiment of the invention depicts a vertical vessel or riser containing solids into which gas is injected and which are maintained in what one would describe as a spouting bed i.e. the particles are suspended or entrained (page 10, lines 10 to 15) in the gas stream such that the particles are carried up the riser and returned to the bottom of the vessel. FIG. 3 designated as 200 appears to clearly depict this. The description which is extremely vague gives little or no indication of the intended process, except that the statement in lines 29 to 31 of page 20 indicates that xe2x80x9cthose elements of the process using the same numerals in the third embodiment as in the second embodiment, are the samexe2x80x9d. This leads one to conclude that the apparatus and operation with minor exceptions are the same since the vessel and collection device have the same numerals as the second embodiment. If however the bed is a spouting bed then the gas stream entering the xe2x80x9cVxe2x80x9d shaped bottom would project the particles into the vessel somewhat like a fountain while the returned particles would follow the sides down to the gas injection point to be projected back into the center portion of the vessel. This is a typical spouting bed rather than a true or conventional fluidized bed. The inventors were obviously aware of this distinction since their description of the fluidization in the heat exchange section 202 feeding the vessel as xe2x80x9ca low velocity bubbling bed of particles of gas as fluidizing mediumxe2x80x9d (p. 21 line 4,9) is typical of true or conventional fluidization.
This description is not applied to either of the two embodiments or the process within the reactor vessel and the fact that the product is removed by gas conveyance out the top of the vessel clearly demonstrates that true or conventional fluidization with its advantages which will be described in the inventive process were not contemplated in this teaching. It is also difficult to determine how the inventors contemplate the process to work since it is not explicitly described. For example, if the spouting bed of particles is retained in the vessel to achieve at least 71-84% yield, it must be retained up to two hours (page 7, line 28) using very fine particles less than 10 microns for reaction 3 (HClg+CaCO3) before the bed is then conveyed to the collection system by a higher velocity gas. During this time frame reaction gas continues to leave the system through the purge orifice and at least in the mid to later stages of the process must contain significant un-reacted HCl and or Cl2 gas due to the lower chloride concentration gradient between the partially reacted product and the gas. The purge gas which will create a serious environment hazard (HCl or Cl2) must be cleaned up before releasing inert gases (air and/or CO2 from the reaction) to the atmosphere adding substantial capital cost to the process.
The process in both of these embodiments appears to be essentially batch processes, that is the bed of solids are fed into the reactor and retained in the reactor for some period of time, while being subjected to a gas containing the reacting medium, until the reaction is close to completion. The product must then be ejected from the vessel by a much higher velocity gas, which must be purged from the system. The inventors appear to have contemplated this mode of operation since on page 20, lines 1-6 they computed the gas velocity needed for so-called xe2x80x9cfluidizationxe2x80x9d for particles less than 10 and 15 microns and for xe2x80x9ccarrying velocityxe2x80x9d.
If on the other hand the process is operated on a continuous basis with raw material being fed into the apparatus, and finished product being removed continuously, then because of the inherent inefficiency of a spouting bed process operated in a continuous fashion and the time required to completely convert the product, the finished product will contain a relatively high percentage of unconverted raw feed and the purge gas a higher percentage of feed gas components. The finished product would of course be a homogeneous blend of unreacted and reacted solids and the purge gas a blend of reacted and unreacted gases. It is obvious from the computations reported (page 20 lines 14-19) that the inventors anticipated a relatively high percentage (up to 10%) of un-reacted calcium carbonate in the finished product of both described xe2x80x9cfluidized processesxe2x80x9d.
If the so-called xe2x80x9cfluidization process are batch rather than continuous they cannot be combined with any other continuous operation producing hydrogen chloride and or chlorine gas unless there are multiple units of the process in operation, so that there is always a unit available to accept gas from the producer of the hydrogen chloride and or chlorine. This is a serious deficiency adding considerable capital cost to any commercial installations.
If on the other hand the solids are entrained by the gas stream in the vessel with part of the feed circulated and part recovered as finished product then the process could be operated in a continuous manner as previously shown but with the serious deficiency of low quality finished product (high percent of initial product) and serious environmental issues (removal of HCl and or Cl2 from purge gas). None of these disadvantages exist in the inventive process due to the use of true fluidization and counter current flow of gas and solids in a continuous process.
The instant invention also eliminates all of the previously outlined disadvantages of the fixed bed embodiment of the Loots and Van Gottberg invention in that the inventive process is continuous and eliminates loading and unloading fixed reactor beds with their attendant high labor cost. Efficient heat exchange between gas and solid effectively uses the heat liberated in the exothermic reaction which together with true fluidization maintains gas and solid temperatures and substantially reduces condensation on the solids of the water produced in the reaction, mitigating conglomeration of the product. This in turn prevents the major problem of removing this fused product and the need to crush or pulverize it. Fines created by pulverization also present serious disposal or sales problems which are not present in the instant invention since large particle-sized feed is possible and which sizing is essentially retained throughout the process. Pressure drop in the process is greatly reduced which reduces power and capital cost in compression equipment. Preheating solids and gas is minimized since the hot gases moving upwardly through the multiple true fluidized beds actively react with the incoming ambient feed and the warm exiting solids react with the incoming ambient gas which not being anhydrous actively reacts with any remaining unreacted solids. In addition the instant process also permits conversion of the solids to the respective halide in a single vessel saving significant capital investment.
The primary object of this invention is to eliminate the operating problems, inefficiencies and environmental deficiencies of the prior art by providing an improved process by which metal oxides, carbonates, bicarbonates and hydroxides may be reacted with hydrogen halides to produce solid compounds containing the halide while liberating water vapor and carbon dioxide depending on the original metal anions.
An object of the present invention is to provide a highly energy efficient process for said reactions by intimately contacting metal, carbonates, bicarbonates, oxides, and hydroxides in a series of conventional or true fluidized beds with reactive hydrogen halide gas in countercurrent flow.
Another object of the invention is to provide a simple, continuous and cost effective process for the manufacture of said compounds.
Another object of the invention is to provide the conditions by which the new process may be effectively performed to produce the said compounds.
Another object of the invention is to provide granular products consisting of approximately the same mesh size as the initial solids and which being of larger size have more commercial value.
Another object of the invention is to provide an economical and effective method to produce commercial grade metal halides with minimal environmental impact.
A final object of the invention is to provide an economical and cost effective method to produce commercial grade calcium chloride with little or no environmental impact.
The invention consists of certain novel claims and a combination of parts hereinafter fully described, illustrated in the accompanying drawings and particularly pointed out in the appended claims, it being understood that changes in the details may be made without departing from the spirit or sacrificing any of the advantages of the present invention.